Increasing demand for renewable energy sources, including ethanol production, has created commercial demand for the generation of ethanol fuel sources. The process to obtain ethanol generally involves the transformation of plant matter, usually sugars, into a distilled pure ethanol product, through either a wet or dry milling processes. Wet milling methods include various soaking steps to soften grains and separate the soluble starches (from the germ, fiber and protein components) for further treatment before alcohol production methods. Dry milling methods are most commonly used for ethanol production, involving the grinding of whole plant matter into meal (without fractionating or separating the various component parts of the starch, as is done with wet milling) and forming a slurry. Subsequently, the starch components of the slurry are converted into sugars, through the use of high temperatures and enzymes, to effectuate the conversion. Upon generation of a sugar source from the plant matter, the conversion to ethanol requires the use of an ethanol-producing microorganism, such as yeasts.
The ethanol-producing microorganism utilized in the fermentation process most often involves yeast added to the mixture to convert sugars to alcohol, which is then distilled, purified, and denatured to generate the ethanol end product. (U.S. Pat. No. 4,316,956). The majority of fuel ethanol is produced by a few distinct strains of yeast. These commercial yeast strains require a high tolerance to both sugars and ethanol in order to yield sufficient ethanol concentrations.
The various processes and method steps for producing ethanol are well known by those skilled in the art and are described in various references. Ethanol production includes at least the following processes or method steps, or combinations of the same: milling, liquefaction, saccharification, fermentation and distillation. (See e.g., U.S. Pat. Nos. 5,231,017 and 4,316,956, WO 94/08027, WO 92/20777). One skilled in the art can ascertain the process for production of ethanol, including for example, whether steps are carried out simultaneously.
Numerous improvements to the ethanol production process, including both the wet and dry milling processes, have been achieved by those skilled in the art. For example: genetic modifications to ethanol-producing microorganisms (see e.g. Shi et al, J. Ind. Microbiol. Biotechnol., 36:139-47 (2009)); improving thermotolerance (see e.g. U.S. Publication No. 2005/0069998); and improved enzymatic processes and enzymes (see e.g. WO 2007/145912).
Despite improvements to methods of ethanol production, the process is complex and the significant commercial interest in ethanol creates a continued need to further improve the production process, including the ethanol-producing microorganisms utilized therein. Accordingly, improvements upon commercial yeasts strains are further necessary to enhance industrial production of ethanol. Ethanol-producing microorganisms, such as yeast, capable of improving ethanol production, as measured by the ability to produce increased ethanol yields, provide both significant economic and industrial advantages. Even slight improvements in ethanol production provide significant commercial benefits. For example, it is estimated that an increased ethanol yield of 1% (estimated as an additional 0.0271 gallons/bushel) generates a commercial value of $100 million dollars annually for the ethanol industry (estimated as $2.00/gallon ethanol).
Accordingly, enhanced methods for ethanol production involving novel, isolated ethanol-producing microorganisms, such as yeast strains, will enhance production and profitability of industrial ethanol production.